The present invention relates to a cooling system of an electronic device having a plurality of circuit boards therein.
In a conventional electronic device in which many circuit boards are installed, the circuit boards are arranged vertically in multiple stages to reduce the signal propagation delay time among the circuit boards.
Referring to FIG. 7, a conventional electronic device 1 comprises a plurality of circuit boards 2, each having a plurality of electronic components such as large-scale integrated circuits (LSIs) and integrated circuits (ICs) thereon, and a cabinet 11 in which these circuit boards 2 are installed in multiple stages arranged vertically. On the bottom of the cabinet 11 is provided an inlet port 3 through which air (cool air) is taken into the cabinet 11; on the top of the cabinet 11 is provided an exhaust port 4 through which air is exhausted from the cabinet 11. In addition, to blow cool air taken in through the inlet port 3 onto the electronic components on the circuit boards 2 and to cool them, a plurality of fans 5 are provided on the inlet port sides of the circuit boards 2.
In the conventional electronic device 1 such as the one described above, the fans 5 take in air through the inlet port 3 into the cabinet 11 to supply it to the plurality of circuit boards 2. The air, warmed by the electronic components on the circuit boards 2, is exhausted from the cabinet 11 through the exhaust port 4.
When the heat generated by the electronic components in the conventional electronic device 1 becomes high, the temperature of the room (hereinafter called "machine room") where electronic device 1 is mounted rises. This warms the air blown by the fans 5 onto the electronic components, making it difficult to cool the electronic components properly.
In such a case, an air conditioning system is usually provided in the machine room to lower the temperature of the air in the room. In a machine room where a large electronic device is installed, the so-called floor air-conditioning system that supplies cool air under the floor is usually used. In this system, air blown up from under the floor cools the inside of the electronic device.
In FIG. 7, the wind speed at arrow X at which cool air is blown up from under the floor is, usually, as high as 2 meter to 3 meter per second. Inside the cabinet 11, the larger the distance from the inlet port 3, the lower the speed of the cool air. That is, the wind speeds inside the cabinet 11 are in order of (wind speed at arrow A)&gt;(wind speed at arrow B)&gt;(wind speed at arrow C). The lower the speed of the cool air that is blown upward, the easier it is to catch the cool air. This means that it is easier for a fan 5C arranged near the top of the cabinet 11 to catch the cool air. Conversely, it is difficult for a fan 5A provided near the bottom of the cabinet 11 to catch the cool air because the speed of the cool air blown upward is high. That is, the amounts of the cool air caught by the fans 5A to 5C and supplied to the circuit boards 2 are in the order of (amount of cool air at arrow C')&gt;(amount of cool air at arrow B')&gt;(amount of cool air at arrow A'). Therefore, the cool air flowing slowly near a circuit board 2a installed near the bottom of the cabinet 11 does not have a sufficient cooling effect as compared with the cool air flowing somewhere else in the cabinet 11. In some cases, the speed of the cool air falls below a predetermined level with the result that the lower-stage circuit board 2A cannot be cooled enough.
In such a case, for blowing a wind at a predetermined speed near the lower-stage circuit board 2A, it is required that the fans 5 are more powerful or a larger distance from the inlet port 3 to the fans 5. However, this configuration makes the fans 5 noisier and the cabinet 11 larger.